外加电位下X80双相管线钢在模拟沿海土壤环境中的应力腐蚀行为

Stress corrosion behavior of X80 dual-phase pipeline steel under applied potential in simulated coastal soil environment

采用交流阻抗谱、极化试验、慢应变拉伸试验研究了不同外加电位下在模拟沿海土壤环境中X80双相管线钢的应力腐蚀行为,对拉伸断口和极化后试样进行SEM表面形貌及能谱分析。结果表明,与慢扫极化(模拟的非裂尖区域)相比,X80双相管线钢快扫极化模拟的裂尖腐蚀电位较负且腐蚀电流较大。-750 mV外加阴极电位处于裂尖自腐蚀电位范围,不足以起到阴极保护的作用,对应力腐蚀仍十分敏感。外加电位为-1050 mV时,阴极反应速率显著大于阳极反应,阴极反应产生的氢被金属吸收且扩散,慢应变拉伸未经颈缩即发生断裂,为准解理断裂。外加阴极电位为-900 mV,阴极电流有效抑制了阳极溶解反应,因此管线钢在模拟沿海土壤溶液中慢应变拉伸抗拉强度和断面收缩率都最高,断口表现为韧性断裂,侧面裂纹细小,阻抗模值最大,应力腐蚀敏感性最小。

Stress corrosion behavior of X80 dual-phase pipeline steel in the simulated coastal soil environment under different applied potentials was studied by AC impedance spectroscopy, polarization test and slow strain rate tensile test. The tensile fracture and polarized specimens were analyzed by SEM and EDS. The results show that the self-corrosion potential of the X80 dual-phase pipeline steel by fast scanning polarization(simulated crack tip) is more negative and the corrosion current is higher than that of polarization at slow scanning rate(simulated non-crack tip area). Applied cathode potential of-750 mV is right about the self-corrosion potential of crack tip, which is not negative enough to play the role of cathodic protection, so that it is still very sensitive to stress corrosion. When the applied potential is^(-1)050 mV, the cathode reaction rate is significantly higher than that of anode reaction, the hydrogen generated by cathode reaction is absorbed and diffuses in the steel, thus the slow strain tensile specimen breaks without necking, with the fracture being quasi cleavage. When the applied cathode potential is-900 mV, the cathode current effectively inhibits the anodic dissolution reaction, and the slow strain tensile strength and the percentage reduction of area of the X80 pipeline steel in coastal soil solution are the highest, the fracture is characterized by ductile fracture, small side cracks, the largest impedance modulus. Therefore the stress corrosion sensitivity of the X80 dual-phase pipeline steel under-900 mV cathodic potential is the smallest.